1. Field of the Invention
The present invention generally relates to a technology for distinguishing a live finger from an artificial finger in a fingerprint authenticating system, even when the artificial finger is made of gummy material.
2. Description of the Related Art
Use of biometric information, such as fingerprints, for performing user authentication is becoming popular. It is said that the user authentication based on the biometric information is more reliable than the conventional method of using passwords or identification (ID) cards; because, while the passwords or the ID cards can be stolen or lost, the biometric information can not be stolen or lost. Even with the biometric information, however, there still is a possibility that a third person can maliciously pass as an authentic person.
In the case of a fingerprint for example, it is not very difficult to prepare an artificial finger that has the same fingerprint as that on a finger of an authentic user, and be successful in the user authentication by using the artificial finger. One approach to prevent that is to differentiate real fingers and artificial fingers, and not allow the use of the artificial fingers in the user authentication.
Artificial fingers can be made of silicon, rubber, gummy material (gelled gelatin solution) and the like. Silicon and rubber do not conduct electricity, so that artificial fingers made of silicon or rubber can be comparatively easily detected with capacitance fingerprint sensors or weak-electric-field fingerprint sensors. The gummy material, however, is very similar to the composition of human epidermis. Furthermore, it conducts electricity, which makes detection of the artificial fingers made of gummy material very difficult.
Japanese Patent Laid-Open Publication No. H2-79181 discloses a technology for differentiating an artificial finger from a real finger for preventing a fraud using an artificial finger made of such as gummy material by applying light in almost normal direction to a surface of an object and referring condition how the light diffuses.
However, even with the above disclosed technology, there still is a problem that detection of counterfeit is difficult when thin artificial fingerprint made of for example, gummy material, is attached to a surface of a real finger. The thin artificial fingerprint is transmissive, so that light can be applied to the surface of the finger through the gummy material and the light is diffused with the same diffusion-pattern as generated from a real finger.